Nature versus Nurture

The overarching theme of the novel is that heredity and environment each contribute to White Fang's fate. London comes down on the side of nurture as being the more powerful force. White Fang's nature is malleable, and he adjusts to whatever conditions his environment presents in order to survive. Under the abuse of Beauty Smith, White Fang becomes a killer seething with hate; under the loving hand of Weedon Scott, he becomes a gentle pet.

While this theme is woven throughout the novel, it is stated explicitly in these lines:

White Fang grew stronger, heavier, and more compact, while his character was developing along the lines laid down by his heredity and his environment. His heredity was a life-stuff that may be likened to clay. It possessed many possibilities, was capable of being moulded into many different forms. Environment served to model the clay, to give...